True gamers that can appreciate and respect a strong gaming engine and solid gameplay experience will go for this game. Sadly, the other end of that spectrum will go for MW3, just because it's Call of Duty. The franchise has a vicegrip on the market. Millions of 12-year-olds will want that fast twitch shooter that is Call of Duty. They'll want to form even more Optic and FaZe fanboy clans. MW3 will outsell B3.
(As a mature, experienced gamer who has experienced both sides, I will opt for MW3. I do not enjoy the type of gameplay Battlefield offers. It's just not my cup of tea.)
I've only just played BFBC2 this past week, and it's a really nice change of pace from playing COD all the time. Was hard to play at first, but I'm quite docile, so it was easy to get used to after about a day or two (but I'm no 3L1T3 8K1LL8 or anything). If I had the money, I'd probably buy BF3.
The grafx are nice, but I think my eyes are still adjusting to the look, because I find it really hard to spot players, unlike in COD. I really dislike conquest, though; rush and TDM are the only ones I play.
MW3 will probably still "beat" BF3 as far as outselling it, though.